Bulb type electrodeless fluorescent lamp

ABSTRACT

A connection wire  110  extends from an end of an induction coil  109,  along a surface of a base portion  104   b  of a bobbin  104,  which surface is located close to a luminous bulb  101.  The connection wire  110  is separated from a sealing portion  118  of an innertube  120  and an outertube  119.

TECHNICAL FIELD

The present invention relates to self-ballasted electrodelessfluorescence, and more particularly relates to self-ballastedelectrodeless fluorescent lamps that can directly replace incandescentlamps.

BACKGROUND ART

Recently, in view of global environmental protection and costeffectiveness, self-ballasted fluorescent lamps with electrodes, whichhave about five times higher efficacy than that of incandescent lamps,have been widely used as substitutes for incandescent lamps in houses,hotels and other places. In addition to the already existingself-ballasted fluorescent lamps with electrodes, self-ballastedelectrodeless fluorescent lamps have also been studied in recent years.A feature of electrodeless fluorescent lamps is that they have a longerlife than fluorescent lamps with electrodes, owing to the absence ofelectrode. Electrodeless fluorescent lamps are thus expected to becomewidespread in the future.

Such a self-ballasted electrodeless fluorescent lamp is disclosed inJapanese Laid-Open Publication No. 10-92391, for example. Theself-ballasted electrodeless fluorescent lamp disclosed in thepublication is illustrated in FIG. 6.

The self-ballasted electrodeless fluorescent lamp 200 of FIG. 6 has asthe entire device the shape of an incandescent lamp. More specifically,the lamp 200 is composed of a translucent discharge vessel 201, a coil203 inserted in a cavity portion 201 a of the discharge vessel 201, anda power supply circuit 204 for supplying alternating current to the coil203. The coil 203 is made up of a rod-shaped ferrite core and a winding.The winding is connected to the power supply circuit 204. The powersupply circuit 204 is formed and vertically placed on a circuit board onwhich a rectifier and a RF oscillator are provided in a verticaldirection in the figure. The power supply circuit 204 is covered with aplastic case 205. Input power to the power supply circuit 204 issupplied via a base 207 provided on part of the case 205.

Mercury amalgam 206 and argon are enclosed as luminous substance in thedischarge vessel 201, while a phosphor layer 202 is formed on the innersurface of the discharge vessel 201. The phosphor layer 202 changesultraviolet light produced in the discharge vessel 201 into visiblelight.

However, to use electrodeless fluorescent lamps as substitutes forincandescent lamps, it is required to make the electrodeless fluorescentlamps closer to the incandescent lamps in terms of outer appearance andsize. When a circuit board is placed vertically as in theabove-mentioned disclosed electrodeless fluorescent lamp, it isdifficult for the lamp to have an outer appearance and a size close tothose of an incandescent lamp. Thus, in order to make the entire sizealmost equal to that of an incandescent lamp and then place the circuitboard therein, the circuit board is preferably placed horizontally. Inview of this, the present inventors have made an electrodelessfluorescent lamp in which a circuit board is placed horizontally andwhich is equal in size to an incandescent lamp.

The present inventors made various experiments using the lamp with thehorizontally placed circuit board, and consequently found that when thelamp is operated, blackening is caused near the opening of the cavityportion of the discharge vessel and that the mercury reacts with thevessel wall and is consumed. Such blackening becomes particularly severewhen a phosphor, a protective coating, or the like is not applied. Thefact that blackening occurs in an inner tube around the winding of aninduction coil has been conventionally known as disclosed in JapaneseLaid-Open Patent Publication No. 11-102667. However, the fact thatblackening occurs in the vicinity of the opening of the cavity portionwas found by the present inventors for the first time. The mechanismbehind the occurrence of blackening of the inner tube around the windingwas that a high electric field, resulting from a potential differencebetween adjacent turns of the winding, causes ions or the like in plasmato be attracted to, and come into collision with, the tube wall. On theother hand, the blackening occurring near the opening of the cavityportion, which was found by the present inventors, is caused in thevicinity of a connection wire that extends from the coil, and cannot beexplained by the mechanism disclosed in the above-mentioned publication,because there are no such adjacent turns. If such blackening occurs, themercury is held in the blackened portion, which causes the problem thatthe quantity of mercury in the discharge gas decreases over the courseof time, so that the quantity of emitted light is reduced. Nevertheless,since the mechanism behind such blackening is unknown, countermeasurescannot be taken easily.

In view of these circumstances, the present invention was made, and anobject thereof is to provide a self-ballasted electrodeless fluorescentlamp in which no blackening occurs near the opening of a cavity portionof a discharge vessel.

DISCLOSURE OF INVENTION

A first inventive self-ballasted electrodeless fluorescent lampincludes: a luminous bulb in which a luminous gas containing at leastmercury is enclosed and which has a cavity portion; an induction coilinserted in the cavity portion; a circuit board electrically connectedto the induction coil; a case in which the circuit board is placed; anda base attached to the case and electrically connected to the circuitboard, wherein a ballast circuit for supplying high frequency power tothe induction coil is formed on the circuit board; the luminous bulbincludes an approximately spherical outer tube and an inner tubedefining the cavity portion; the circuit board is placed approximatelyhorizontally when a central axis of the inner tube is placed vertically;a connection wire for electrically connecting the induction coil and thecircuit board extends from one end of the induction coil into a regionbeyond an outer edge of the cavity portion, and is connected to thecircuit board; and the connection wire is placed so as to be spacedapart from a sealing portion of the outer and inner tubes.

The self-ballasted electrodeless fluorescent lamp preferably furtherincludes: a bobbin including a winding rod, around which the inductioncoil is wound, and a base portion, which is placed approximately at aright angle with respect to the winding rod and which supports thewinding rod. And, preferably, the winding rod of the bobbin is insertedin the cavity portion; the base portion of the bobbin is disposedbetween the luminous bulb and the circuit board; and the connection wireextends from the one end of the induction coil so as to pass on or abovea surface of the base portion which is located close to the luminousbulb.

In the self-ballasted electrodeless fluorescent lamp, part of the casepreferably supports part of the luminous bulb, and the structure inwhich the connection wire is disposed spaced apart from the sealingportion is preferably realized by lifting with the case the luminousbulb in a direction opposite to the base.

In the self-ballasted electrodeless fluorescent lamp, an upper end ofthe case preferably supports part of the luminous bulb in such a manneras to lift the luminous bulb in a direction opposite to the base,thereby allowing the connection wire to be disposed spaced apart fromthe sealing portion.

In the self-ballasted electrodeless fluorescent lamp, a protrusion,which supports part of the luminous bulb in such a manner as to lift theluminous bulb in a direction opposite to the base, is preferably formedon the base portion, which allows the connection wire to be disposedspaced apart from the sealing portion

In the self-ballasted electrodeless fluorescent lamp, a film capacitor,which is a circuit element included in the ballast circuit, ispreferably disposed on a surface of the circuit board which is locatedclose to the base

A second inventive self-ballasted electrodeless fluorescent lampincludes: a luminous bulb in which a luminous gas containing at leastmercury is enclosed and which has a cavity portion; an induction coilinserted in the cavity portion; a circuit board electrically connectedto the induction coil; a case in which the circuit board is placed; anda base attached to the case and electrically connected to the circuitboard, wherein a ballast circuit for supplying high frequency power tothe induction coil is formed on the circuit board; the luminous bulbincludes an outer tube and an inner tube defining the cavity portion;the circuit board is provided with output terminals to the inductioncoil and input terminals from the base; the output and input terminalsare disposed so as to be separate from each other by 15 mm or more; aconnection wire for electrically connecting the induction coil and thecircuit board extends from one end of the induction coil into a regionbeyond an outer edge of the cavity portion, and is connected to thecircuit board; and the connection wire is placed so as to be spacedapart from a sealing portion of the outer and inner tubes.

In one preferred embodiment, the connection wire and the sealing portionare spaced apart from each other by 0.3 mm or more.

In one preferred embodiment, the greatest length of the circuit board is60 mm or less.

A phosphor or a protective coating is not applied to an inner wall ofthe sealing portion.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a partially cutaway view of a self-ballasted electrodelessfluorescent lamp in accordance with a first embodiment.

FIG. 2 is a partially cutaway view of a self-ballasted electrodelessfluorescent lamp in accordance with a second embodiment.

FIG. 3 is a view illustrating a circuit board surface that is locatedclose to a luminous bulb in accordance with the first embodiment.

FIG. 4 illustrates the external appearance of the self-ballastedelectrodeless fluorescent lamp of the first embodiment.

FIG. 5 is an exploded view of the self-ballasted electrodelessfluorescent lamp of the first embodiment.

FIG. 6 is a view schematically illustrating a conventional electrodelessfluorescent lamp.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described withreference to the accompanying drawings. In the drawings, members thathave substantially the same function will be identified by the samereference numerals for the sake of simplicity. The present invention isnot limited to the following embodiments.

First Embodiment

FIG. 1 is a partially cutaway view of a self-ballasted electrodelessfluorescent lamp in accordance with a first embodiment. Theself-ballasted electrodeless fluorescent lamp illustrated in FIG. 1, towhich electric power can be supplied via the base, includes a ballastcircuit.

The self-ballasted electrodeless fluorescent lamp includes a luminousbulb (bulb) 101 having a cavity portion (cavity), an induction coil 109inserted in the cavity portion 120, a circuit board 105 electricallyconnected to the induction coil 109, a case 106 in which the circuitboard 105 is placed, and a base 107 electrically connected to thecircuit board 105. In the luminous bulb 101, a luminous gas containingat least mercury is enclosed. The base 107 is attached to the case 106.The luminous bulb 101, the induction coil 109, the circuit board 105,the case 106, and the base 107 are integrated into one unit.

The induction coil 109 functions as a high frequency electromagneticfield generating means for generating a high frequency electromagneticfield within the luminous bulb 101. The induction coil 109 is composedof a core (not shown) made of soft magnetic material (ferrite, forexample) and a coil (excitation coil) 103 wound around the core. In thisembodiment, the core is placed within a cylindrical winding rod 104 a ofa bobbin 104, and the excitation coil 103 is also wound around thewinding rod 104 a. The coil 103 of the induction coil 109 iselectrically connected to the circuit board 105 via a connection wire110. On the circuit board 105, a ballast circuit for supplying highfrequency power to the induction coil 109 is formed.

In this embodiment, the luminous bulb 101 is composed of a substantiallyspherical outer tube 119 and an inner tube 120 that defines the cavityportion. The inner tube 120 is approximately cylindrical and has anopening in vicinity to the circuit board 105. The outer tube 119 is inthe shape of a so-called eggplant-shape. Examples of such a shapeinclude the A-shape defined in JIS C 7710-1988.

As shown in FIG. 1, the connection wire 110 is disposed spaced apartfrom a sealing portion 118 of the outer and inner tubes 119 and 120. Theluminous bulb 101 is supported by an upper end 106 a of the case 106,which is the end opposing the base 107. The case's upper end 106 abrings the luminous bulb 101 upward in such a manner that the connectionwire 110 extending along the base portion 104 b of the bobbin 104 isspaced apart from the sealing portion 118 of the outer and inner tubes119 and 120. In this embodiment, the connection wire 110 extends from anend of the excitation coil 103 and is part of the excitation coil 103.However, the connection wire 110 is not limited to being part of theexcitation coil 103 in this manner, but a conductive member such as acopper wire, a copper sheet, or a corrosion-inhibitor-plated coppersheet may be used. In that case, such a connection wire may beelectrically connected with the excitation coil 103.

In this embodiment, the connection wire 110 is disposed spaced apartfrom the sealing portion 118 in order to prevent blackening of the innerwall of the sealing portion 118. Although mechanisms behind theoccurrence of such blackening have not been elucidated sufficiently, thepresent inventors' thinking concerning the mechanisms is as follows.More specifically, if the connection wire 110 is in contact with thesealing portion 118, a potential difference occurring during lampoperation between plasma within the luminous bulb 101 and the connectionwire 110 causes ions in the plasma to be attracted toward the connectionwire 110 and then react with the material of the luminous bulb 101 toform mercury amalgam, thereby resulting in blackening. This ispresumably due to the fact that the connection wire 110 is located tooclose to, and thus in contact with, the sealing portion 118, because ofthe circuit design of the horizontally placed circuit board 105, as willbe described later. The problem of blackening can thus be solved byseparating these members from each other. It would be considered thatcoating the inner wall of the luminous bulb 101 with a protectivecoating or a phosphor for suppressing the mercury reaction could preventthe blackening easily. However, since the sealing portion 118 is aportion in which the glasses fuse together, such a coating cannot beapplied to the inner wall of the sealing portion 118. Therefore, it ispresumed that if the sealing portion 118 and the connection wire 110 arenot separate from each other unlike in this embodiment, the sealingportion 118 will be easily blackened. The protective coating mentionedin this embodiment includes alumina particles, for example. Aluminaparticles suppress sodium diffusion from the glasses to react with themercury.

Next, the structure of this embodiment will be further described indetail. The luminous bulb 101 is a vessel made of glass in which mercuryas luminous material and a rare gas (e.g., krypton or argon) as a buffergas are enclosed. The mercury, which is enclosed in the luminous bulb101 in a liquid form or as amalgam, is heated by plasma produced duringlamp operation, and the luminous bulb 101 has a mercury vapor pressuredefined by that temperature. The internal volume of the luminous bulb101 is, for example, from 100 to 270 cm³. In the luminous bulb 101, themercury is enclosed in an amount of 2 to 10 mg, and the krypton isenclosed at a charged pressure of 50 to 300 Pa (at a temperature of 25°C.)

A phosphor 102 for converting ultraviolet light produced by dischargewithin the luminous bulb 101 into visible light is applied to the inside(the inner wall) of the luminous bulb 101. As described above, the innertube 120 that is the cavity portion, into which part (i.e., theinduction coil) of the high frequency electromagnetic field generatingmeans is inserted, is formed in part of the luminous bulb 101. It isthus easy to dispose the high frequency electromagnetic field generatingmeans near the luminous bulb 101. The luminous bulb 101 is formed of thecylindrical inner tube 120, in which the excitation coil 103 can bedisposed, and the approximately spherical outer tube 119 with thephosphor 102 applied thereto. The outer edge of the cavity portion ofthe inner tube 120 is melted with flame from a burner or the like andfused to part of the outer tube 119. This fused portion is the sealingportion 118, and the phosphor 102 is not applied to the sealing portion118. Since the fusing of this portion is carried out in the last stageof the fabrication of the luminous bulb 101, it is not possible to applythe phosphor 102.

Exemplary dimensions or the like of the luminous bulb 101 of thisembodiment are as follows. The outer diameter of the central portion ofthe luminous bulb 101 (that is, the outer diameter of the greatestportion) is from 50 to 90 mm (thickness: about 1 mm). The luminous bulb101 is made of soda lime glass, for example, but may be made ofborosilicate glass or the like. The height of the luminous bulb 101 andthe height of the electrodeless fluorescent lamp including the base 107are, for example, from 60 to 80 mm, and from 130 to 240 mm,respectively. The inner diameter of the inner tube 120 of the luminousbulb 101 is, for example, from 16 to 26 mm.

The ballast circuit connected to the excitation coil 103 located in theinner tube 120 supplies high frequency power to the excitation coil 103.In other words, the ballast circuit is a high frequency power supply. Inthis embodiment, the high frequency electromagnetic field generatingmeans is composed of the high frequency power supply, the ferrite core,and the excitation coil 103 wound around the ferrite core. As shown inFIG. 1, to produce discharge in the luminous bulb 101, the highfrequency electromagnetic field generating means (in particular, theexcitation coil 103 and the ferrite core) is provided in substantiallythe central portion of the luminous bulb 101. More specifically, theferrite core and the excitation coil 103 wound around the bobbin 104 areinserted in the inner tube 120 of the luminous bulb 101. The circuitboard 105, on which the high frequency power supply (ballast circuit) isformed, is placed in the case 106, and power is supplied from anexternal device via the base 107. The base 107 is structured so as to bescrewed into a socket, so that just screwing the base 107 into a socketallows the electrodeless fluorescent lamp to be electrically connectedto an external power supply (for example, commercial power.) Moreover,not only the electrodeless fluorescent lamp can be used just by screwingthe base into a socket, but also the size and outer appearance of thelamp are close to those of an incandescent lamp. The electrodelessfluorescent lamp can therefore be put to the same uses as anincandescent lamp, and thus can directly replace an incandescent lamp.

The bobbin 104 is composed of the winding rod 104 a and the base portion104 b. The excitation coil 103 of the induction coil 109 is wound aroundthe winding rod 104 a. The base portion 104 b is disposed substantiallyat a right angle to the winding rod 104 a and supports the winding rod104 a. The winding rod 104 a has a cylindrical shape and is insertedinto the inner tube 120, which is the cavity portion. The base portion104 b extends from an end of the winding rod 104 a located close to thebase 107, substantially at a right angle with respect to the winding rod104 a, so as to have the shape of a disc. The base portion 104 b ispositioned between the luminous bulb 101 a and the circuit board 105.The base portion 104 b is disposed approximately horizontally, when thecentral axis of the inner tube 120 is placed vertically.

The circuit board 105 is typically a printed circuit board. In thisembodiment, like the base portion 104 b of the bobbin 104, the circuitboard 105 is disposed substantially horizontally when the central axisof the inner tube 120 is placed vertically. The base portion 104 b andthe circuit board 105 are substantially parallel to each other. Thespace in the case 106 is divided into two by the circuit board 105. Thespace on the circuit board 105 which is closer to the luminous bulb 101is in close vicinity to high-temperature plasma in the luminous bulb101, and thus has a higher temperature than the space under the circuitboard 105 which is close to the base 107. Therefore, on the surface ofthe circuit board 105 which is close to the luminous bulb 101,relatively high-temperature-resistant circuit elements such as resistorsare provided, while on the surface thereof close to the base 107, lowheat-resistant circuit elements such as a film capacitor 115 aredisposed. The circuit elements provided on both surfaces and circuitwiring formed on the circuit board 105 form the ballast circuit. Thereason why the film capacitor 115 is used as a capacitor is that ascompared with a ceramic capacitor, change in the capacitance of the filmcapacitor 115 with temperature is smaller, and the film capacitor 115produces a smaller amount of heat because its resistance is lower.

The connection wire 110, which electrically connects the induction coil109 and the circuit board 105, extends from the one end of the inductioncoil 109 into a region beyond the outer edge of the cavity portion, andis connected to the circuit board 105. More specifically, the connectionwire 110 extends from the lower end of the excitation coil 103 of theinduction coil 109, along the winding rod 104 a to the base 107, andthen extends along the surface of the base portion 104 b which islocated close to the luminous bulb 101, in a direction going away fromthe central axis of the luminous bulb 101 (this central axissubstantially agrees with the central axis of the inner tube 120). Theconnection wire 110 then passes through the base portion 104 b near theouter edge of the base portion 104 b, and then extends to the circuitboard 105 for connection with the circuit board 105. In this embodiment,the region beyond the outer edge of the cavity portion is a region whichis located farther away from the central axis of the inner tube 120 thanthe edge of the opening of the inner tube 120 is. More specifically, anexample of such a region may be the sealing portion 118. The connectionwire 110 is disposed so as to separate from the sealing portion 118 ofthe outer and inner tubes 119 and 120. A distance L between theconnection wire 110 and the outer surface of the sealing portion 118 is0.5 mm. The distance L is preferably equal to or greater than 0.3 mm,and more preferably, the distance L is 0.5 mm or greater, in which caseblackening can be prevented more reliably. Furthermore, it is preferablethat insulating, high heat-resistant silicon or the like be applied tothe gap between the connection wire 110 and the sealing portion 118,because the distance L can then be reliably obtained.

The connection wire 110 extends along the base portion 104 b surfaceclose to the luminous bulb 101 in the direction going away from thecentral axis of the luminous bulb 101. Another structure would beconsidered, in which the connection wire 110 extending along the windingrod 104 a would pass through the base portion 104 b where the connectionwire 110 reaches the base portion 104 b, and then would extend along thesurface of the base portion 104 b which is close to the circuit board105, in a direction going away from the central axis of the luminousbulb 101. However, this structure is not desirable because of thefollowing reasons. On the circuit board 105 surface close to the baseportion 104 b, there are the circuit wiring, the circuit elements, andprotrusions of terminals of the circuit elements disposed on theopposite surface thereof. The connection wire 110 may thus be in contactwith those members to be short-circuited or discharge.

FIG. 3 schematically illustrates the circuit board 105 surface that islocated close to the luminous bulb 101. The circuit board 105 is anoctagonal sheet, and its greatest length R is 45 mm. The greatest lengthR is the greatest length within the face on which the ballast circuit isformed. The greatest length R, which is normally represented as thediameter of the circumscribed circle of the circuit board 105, ispreferably 60 mm or less, so that the circuit board 105 can behorizontally placed within the case 106. The circuit board 105 may beround or rectangular in shape. Circuit elements 131, 131, . . . such asresistors are disposed on the surface of the circuit board 105, andconnected via circuit wires 132, 132, . . . to the terminals 133, 133, .. . of circuit elements formed on the opposite surface. Two outputterminals 134, 134 to the induction coil 109, that is, connectionportions to the connection wire 110, are formed spaced apart from eachother in the vicinity of the outer edge of the circuit board 105. Inputterminals 135, 135 from the base 107 are formed substantially opposingthe output terminals 134, 134 with the center of the circuit board 105between. A distance D between the output terminals 134, 134 and theinput terminals 135, 135 is 23 mm. The distance D is preferably 15 mm ormore.

The greater the distance D becomes the better, because if the outputwiring to the induction coil 109 is located near the input wiring from acommercial power, high frequency noise will be sent to the commercialpower. However, the size of the circuit board 105 is limited, and thatsize determines an upper limit.

Moreover, another constraint that the design of the ballast circuit issubject to is that the output wiring, to which high voltage is applied,should be disposed as far as possible away from the other wires. Due tothis constraint, the output terminals 134, 134, which are the connectionportions with the connection wire 110 to the induction coil 109, areprovided at the edge of the horizontally placed circuit board 105. Theconnection wire 110 thus extends toward the cavity portion, from theedge of the circuit board 105 that is adjacent to the case 106, andwould be in contact with the sealing portion 118, if no countermeasureis taken. In view of this, in this embodiment, the luminous bulb 101 islifted with the case's upper end 106 a to allow the connection wire 110to extend along the bobbin's base portion 104 b so as to be spaced apartfrom the sealing portion 118, thereby preventing blackening of thesealing portion.

The case 106 is made of heat-resistant material, and in this embodimentthe case 106 is made of heat-resistant resin (for example, poly-butyleneterephthalate). The case 106 can be made of material having excellentthermal conductivity (for example, metal) to have increased heatdissipation characteristics.

Next, the outer appearance and configuration of the self-ballastedelectrodeless fluorescent lamp of this embodiment will be described withreference to FIGS. 4 and 5.

The external appearance of the self-ballasted electrodeless fluorescentlamp of this embodiment is composed of the luminous bulb 101, the case106 and the base 107. The case 106 has a threaded structure at one end,and the base 107 with a corresponding threaded structure can be attachedto that one end of the case 106. The ferrite core 117 is inserted in thebobbin 104.

In this embodiment, one end of the bobbin 104 is located in the case106, and a heat sink 116 is attached to that one end of the bobbin 104.The heat sink 116 is, for example, a sheet member with relatively highthermal conductivity (such as metal sheet, ferrite disc.) The heat sink116 attached to the bobbin 104 suppresses temperature increase in theferrite core 117. If the ferrite core 117 exceeds the Curie temperature,the ferrite core 117 no longer functions as a magnetic material, so heatdissipation performed by the heat sink 116 can be a critical matterdepending on the use conditions.

Furthermore, a circuit holder 108, on which the circuit board 105 can beheld, is integrated into the bobbin 104 by interfitting.

Next, it will be briefly described how the self-ballasted electrodelessfluorescent lamp of this embodiment operates. When commercial AC poweris supplied to the high frequency power supply via the base 107, thehigh frequency power supply 105 converts the commercial AC power intohigh frequency AC power, and supplies the high frequency AC power to theexcitation coil 103. The frequency of alternating current supplied bythe high frequency power supply is from 50 to 500 kHz, for example,while the power supplied by the high frequency power supply is from 5 to200 W, for example. Upon receiving the supply of the high frequency ACpower, the excitation coil 103 forms a high frequency AC magnetic fieldin a space close to the excitation coil 103. Then, an induction fieldoccurs perpendicularly with respect to the high frequency AC magneticfield, causing the luminous gas inside the luminous bulb 101 to beexcited to emit light. As a result, light emission in the ultravioletrange or the visible range can be obtained. The light emission in theultraviolet range is changed to light emission (visible light) in thevisible range by the phosphor 102 formed on the inner wall of theluminous bulb 101. It should be noted that the lamp can be configuredwithout forming the phosphor 102 so that the light emission in theultraviolet range (or the light emission in the visible range) isutilized as it is. The light emission in the ultraviolet range isproduced mainly from the mercury. More specifically, when a highfrequency current is applied to the induction coil 109 located in closevicinity to the luminous bulb 101, an induction field formed by magneticforce lines resulting from the electromagnetic induction causescollision between the mercury atoms and electrons in the luminous bulb101, whereby ultraviolet light can be obtained from the excited mercuryatoms.

Now, the frequency of the alternating current that the high frequencypower supply supplies will be described. In this embodiment, thefrequency of the alternating current supplied by the high frequencypower supply is in a relatively low frequency range at or below 1 MHz(for example, from 50 to 500 kHz), as compared with 13.56 MHz or severalMHz in the ISM band generally used in practical applications. Thefrequency in the low frequency range is used for the following reasons.First, if the lamp is operated in a relatively high frequency range,such as 13.56 MHz or several MHz, the size of a noise filter forsuppressing line noise produced by the high frequency power supply isincreased, resulting in an increase in the volume of the high frequencypower supply. Moreover, if noise radiated or transmitted from the lampis at high frequency, an expensive shield has to be used in order tomeet the requirements of strict regulations specified in the law forhigh frequency noise, and this becomes a major obstacle in achievingcost reduction. On the other hand, when the lamp is operated in thefrequency range from about 50 kHz to about 1 MHz, low-costgeneral-purpose products that are used as electronic components forgeneral electronic equipment can be used as components of the highfrequency power supply 105, and in addition, those components can besmall in size. This brings great advantages such as cost reduction andminiaturization. However, the self-ballasted electrodeless fluorescentlamp of this embodiment is not limited to operation at a frequency of 1MHz or less and is capable of being operated at any frequency in afrequency range, within which 13.56 MHz or several MHz, e.g., fall.

In the configuration of this embodiment, the connection wire 110 thatsupplies high frequency power to the induction coil 109 is spaced apartfrom the sealing portion 118 of the inner and outer tubes 120 and 119 ofthe luminous bulb 101. This prevents occurrence of blackening of theinner wall of the sealing portion 118 when the self-ballastedelectrodeless fluorescent lamp is operated.

Furthermore, in this embodiment, the upper end 106 a, which is part ofthe case 106, supports and brings upward the luminous bulb 101, suchthat the connection wire 110 is spaced apart from the sealing portion118. In this manner, the spacing can be realized easily without causingan increase in the number of components. And if each component has highdimension accuracy, the spacing can be reliably achieved just byattaching the case 106. In this embodiment, the entire upper end 106 aof the case supports the luminous bulb 101. Nevertheless, part of thecase's upper end 106 a may support the luminous bulb 101, or asupporting member, such as a protrusion, for supporting and bringingupward the luminous bulb 101 may be provided on the inner surface of thecase 106. It should be noted that the case 106 and the luminous bulb 101may each have a fit portion so as to be fitted into each other.

It should be noted that the connection wire 110 that extends from theone end of the excitation coil 103, along the surface of the bobbin'swinding rod 104 a is also preferably spaced apart from the inner wall ofthe inner tube 120. The distance is preferably 0.3 mm or more.

Moreover, the circuit board 105 may be placed vertically, if theconnection wire 110 extends into a region beyond the outer edge of thecavity portion for connection with the circuit board 105, and is spacedapart from the sealing portion 118.

In addition, if the bobbin 104 is employed as in this embodiment, theexcitation coil 103 and the ferrite core 117 can be disposed within theinner tube 120 of the luminous bulb 101 just by inserting into the innertube 120 the bobbin 104 having the excitation coil 103 wound around thewinding rod 104 a, and by inserting the ferrite core 117 into thewinding rod 104 a. This allows the electrodeless fluorescent lamp to beassembled easily. If the bobbin 104 and the luminous bulb 101 arefurnished with protrusions, claws, interfitting cavity portions, or thelike for firmly securing the bobbin 104 and the luminous bulb 101 toeach other, and are held together by interfitting, for example, arelative position between the induction coil 109 and the luminous bulb101 can be kept constant, even if, e.g., vibration occurs. Moreover, thewinding rod 104 a and the base portion 104 b are configured as one unit,which suppresses an increase in the number of components.

Second Embodiment

With reference to FIG. 2, a self-ballasted electrodeless fluorescentlamp in accordance with a second embodiment of the present inventionwill be described. The self-ballasted electrodeless fluorescent lamp ofthis embodiment differs from the lamp of the first embodiment only interms of configuration for supporting the luminous bulb 101. Therefore,this difference will only be explained.

In this embodiment, a luminous bulb 101 is supported and brought upwardby protrusions 125 formed on a base portion 104 b of a bobbin 104,whereby a connection wire 110 is spaced apart from a sealing portion118. This structure prevents, as in the first embodiment, occurrence ofblacking of the inner wall of the sealing portion 118 when theself-ballasted electrodeless fluorescent lamp is operated. There is agap between a case's upper end 106 a and the luminous bulb 101. This gapmay be filled with a high-temperature resistant adhesive such assilicon.

The shape and number of protrusions 125 supporting the luminous bulb 101are not particularly limited. The base portion 104 b may have a shape inwhich most part of the base portion 104 b rises except for its part onwhich the connection wire 110 extends. Furthermore, the luminous bulb101 may be supported by both the case's upper end 106 a and theprotrusions 125. The shape of the outer tube 119 is not limited to theA-shape. For example, even if the outer tube 119 is approximatelycylindrical in shape, the effects of the present invention can beattained so long as the connection wire 110 extends beyond the sealingportion 118.

While the present invention has been shown in several forms as describedin the preferable embodiments thereof, it is not so limited butsusceptible of various changes and modifications.

The electrodeless fluorescent lamp disclosed in Japanese Laid-OpenPublication No. 10-92391 (see FIG. 6), in which the circuit board isplaced vertically (in a direction parallel to the central axis of theluminous bulb) does not serve as a replacement for an incandescent lamp,because the case in which the circuit board is placed is increased inlength, such that the electrodeless fluorescent lamp is not close to anincandescent lamp in terms of outer appearance and size. Moreover,because of the vertically placed circuit board, ambient temperatureinside the case produced by high temperature plasma within the luminousbulb is almost the same anywhere in the case in spite of differencecaused by convention. It is thus difficult to use low heat-resistantcircuit elements such as film capacitors.

In the present invention, the circuit board is placed horizontally, andthe connection wire of the induction coil is spaced apart from thesealing portion of the inner and outer tubes of the luminous bulb. Thisallows the lamp to have such size and external appearance as to enablethe lamp to become a replacement for an incandescent lamp, whilesuppressing blackening of the sealing portion.

INDUSTRIAL APPLICABILITY

According to the present invention, by a simple structure, anelectrodeless fluorescent lamp that has almost the same size andexternal appearance as those of an incandescent lamp can be obtained,and blackening of a sealing portion can be prevented. Accordingly, thepresent invention has a high industrial applicability in application oflong-life self-ballasted electrodeless fluorescent lamps that canreplace incandescent lamps.

1. A self-ballasted electrodeless fluorescent lamp, comprising: aluminous bulb in which a luminous gas containing at least mercury isenclosed and which has a cavity portion; an induction coil inserted inthe cavity portion; a circuit board electrically connected to theinduction coil; a case in which the circuit board is placed; and a baseattached to the case and electrically connected to the circuit board,wherein a ballast circuit for supplying high frequency power to theinduction coil is formed on the circuit board; the luminous bulbincludes an approximately spherical outer tube and an inner tubedefining the cavity portion; the circuit board is placed approximatelyhorizontally when a central axis of the inner tube is placed vertically;a connection wire for electrically connecting the induction coil and thecircuit board extends from one end of the induction coil into a regionbeyond an outer edge of the cavity portion, and is connected to thecircuit board; and the connection wire is placed so as to be spacedapart from a sealing portion of the outer and inner tubes.
 2. Theself-ballasted electrodeless fluorescent lamp of claim 1, furthercomprising: a bobbin including a winding rod, around which the inductioncoil is wound, and a base portion, which is placed approximately at aright angle with respect to the winding rod and which supports thewinding rod, wherein the winding rod of the bobbin is inserted in thecavity portion; the base portion of the bobbin is disposed between theluminous bulb and the circuit board; and the connection wire extendsfrom the one end of the induction coil so as to pass on or above asurface of the base portion which is located close to the luminous bulb.3. The self-ballasted electrodeless fluorescent lamp of claim 1, whereinpart of the case supports part of the luminous bulb, and the structurein which the connection wire is disposed spaced apart from the sealingportion is realized by lifting with the case the luminous bulb in adirection opposite to the base.
 4. The self-ballasted electrodelessfluorescent lamp of claim 1, wherein an upper end of the case supportspart of the luminous bulb in such a manner as to lift the luminous bulbin a direction opposite to the base, thereby allowing the connectionwire to be disposed spaced apart from the sealing portion.
 5. Theself-ballasted electrodeless fluorescent lamp of claim 2, wherein aprotrusion, which supports part of the luminous bulb in such a manner asto lift the luminous bulb in a direction opposite to the base, is formedon the base portion, which allows the connection wire to be disposedspaced apart from the sealing portion.
 6. The self-ballastedelectrodeless fluorescent lamp of claim 1, wherein a film capacitor,which is a circuit element included in the ballast circuit, is disposedon a surface of the circuit board which is located close to the base. 7.A self-ballasted electrodeless fluorescent lamp, comprising: a luminousbulb in which a luminous gas containing at least mercury is enclosed andwhich has a cavity portion; an induction coil inserted in the cavityportion; a circuit board electrically connected to the induction coil; acase in which the circuit board is placed; and a base attached to thecase and electrically connected to the circuit board, wherein a ballastcircuit for supplying high frequency power to the induction coil isformed on the circuit board; the luminous bulb includes an outer tubeand an inner tube defining the cavity portion; the circuit board isprovided with output terminals to the induction coil and input terminalsfrom the base; the output and input terminals are disposed so as to beseparate from each other by 15 mm or more; a connection wire forelectrically connecting the induction coil and the circuit board extendsfrom one end of the induction coil into a region beyond an outer edge ofthe cavity portion, and is connected to the circuit board; and theconnection wire is placed so as to be spaced apart from a sealingportion of the outer and inner tubes.
 8. The self-ballastedelectrodeless fluorescent lamp of claim 1, wherein the connection wireand the sealing portion are spaced apart from each other by 0.3 mm ormore.
 9. The self-ballasted electrodeless fluorescent lamp of claim 1,wherein the greatest length of the circuit board is 60 mm or less. 10.The self-ballasted electrodeless fluorescent lamp of claim 1, wherein aphosphor or a protective coating is not applied to an inner wall of thesealing portion.
 11. The self-ballasted electrodeless fluorescent lampof claim 7, wherein the connection wire and the sealing portion arespaced apart from each other by 0.3 mm or more.
 12. The self-ballastedelectrodeless fluorescent lamp of claim 7, wherein the greatest lengthof the circuit board is 60 mm or less.
 13. The self-ballastedelectrodeless fluorescent lamp of claim 7, wherein a phosphor or aprotective coating is not applied to an inner wall of the sealingportion.